The PEG (polyethylene glycol) protects the molecule from proteolytic breakdown and increases the biological
half-
life of the interferon protein"
http://en.wikipedia.org/wiki/Peginterferon_alfa-2b
" In Pegasys, a large, branched, mobile PEG is attached to the interferon alfa-2a molecule, providing a selectively protective barrier against rapid absorption, metabolism and elimination"
http://www.medilexicon.com/drugs/pegasys.php
Well, you asked.